A novel function of poly(ADP-ribose) polymerase-1 in modulation of autophagy and necrosis under oxidative stress.

Under oxidative stress, poly(ADP-ribose) polymerase-1 (PARP-1) is activated and contributes to necrotic cell death through ATP depletion. On the other hand, oxidative stress is known to stimulate autophagy, and autophagy may act as either a cell death or cell survival mechanism. This study aims to explore the regulatory role of PARP-1 in oxidative stress-mediated autophagy and necrotic cell death. Here, we first show that hydrogen peroxide (H(2)O(2)) induces necrotic cell death in Bax-/- Bak-/- mouse embryonic fibroblasts through a mechanism involving PARP-1 activation and ATP depletion. Next, we provide evidence that autophagy is activated in cells exposed to H(2)O(2). More importantly, we identify a novel autophagy signaling mechanism linking PARP-1 to the serine/threonine protein kinase LKB1-AMP-activated protein kinase (AMPK)-mammalian target of rapamycin (mTOR) pathway, leading to stimulation of autophagy. Finally, we demonstrate that autophagy plays a cytoprotective role in H(2)O(2)-induced necrotic cell death, as suppression of autophagy by knockdown of autophagy-related gene ATG5 or ATG7 greatly sensitizes H(2)O(2)-induced cell death. Taken together, these findings demonstrate a novel function of PARP-1: promotion of autophagy through the LKB1-AMPK-mTOR pathway to enhance cell survival in cells under oxidative stress.